1. Field of the Invention
The present invention relates generally to gravity simulation systems and, more specifically, to an active response gravity offload system and method for performing reduced gravity testing with robotic systems and humans.
2. Background of the Invention
Various types of reduced gravity or microgravity systems have been used in the past, some of which are discussed below. These systems may provide helpful results in certain ways but are limited in other ways.
The National Aeronautics and Space Administration (NASA) has utilized a number of different types of gravity simulation systems. A Reduced Gravity Simulator utilized at Langley Research Center suspended an astronaut at an angle of 80.5 degrees so that only ⅙th of their weight was supported by the ground while the rest was supported by a pulley system. The Reduced Gravity Simulator only allowed motion in one dimension and the pulleys were uncomfortable and were not able to support every part of the body.
Another system, a partial gravity simulator (POGO), utilized an air controlled piston along with air bearings and gimbals to simulate reduced gravity. POGO used an air-bearing rail to allow for maneuverability in two dimensions. POGO was used to train astronauts how to use tools and other hardware in reduced gravity. POGO, although adding another dimension for motion, induced significant inertial loads on the users. The friction within the system along with the mass, created for less than perfect simulations. Also, the system did not match the dynamics of the person moving and limited their range of motion.
It was found that reduced gravity could be simulated on an airplane flying parabolic trajectories. Using a C-9 aircraft, Lunar, Martian, and microgravity can each be simulated. Some of the downsides to this method include: (1) limited space within the aircraft to move around, (2) simulated environments are only possible for 20-30 second intervals, (3) cost, and (4) the accuracy of the simulated gravity is dependent upon the precision in which the parabolas are flown.
More recently, a first generation Active Response Gravity Offload System (ARGOS) system has been used by NASA. This system utilized a moveable beam in a framework with a winch that supports a cable. The system allows movement in three dimensions. The first generation frame was limited in size but did provide useful simulations. While the first generation ARGOS system showed the concept is viable for use with a larger frame than used in the first generation ARGOS system, numerous problems were apparent for both the vertical and horizontal control systems that would potentially limit the realism of the simulation. The smaller frame of the first generation system effectively hid some problems that become more apparent with a larger framework.
In the vertical control system, for example, force data from a commercial off the shelf (COTS) analog load cell is placed in-line on the lifting cable as the primary feedback device for the vertical system. There are many sources of noise in the load cell data, which impact the resolution and fine control capability of the system. These sources of noise include electronic noise in the load cell, physical vibrations from the hoist gear train, vibrations from the horizontal system, and vibrations from the test participant attached to the system. Many of these sources of noise reside in the same frequency range that the system controls, rendering conventional noise filtering techniques unhelpful. In addition, the ARGOS system should respond fairly quickly to the pertinent signal, while filtering the noise, and cannot tolerate a large amount of response lag, which can cause the system to lose stability.
For the horizontal control system of the first generation ARGOS system, the control input was feedback from a cable angle laser sensor. The control output was an acceleration command to the motor controller, which commands x and y horizontal motors to move in a predetermined x and y axis, respectively. While the first generation ARGOS framework was relatively small and the control motors were relatively slow, unrealistic swinging motion can occur in a frame that is considerably larger than the first generation system, especially in response to human loads that jump or move. The angle laser sensor itself can introduce bias if the cable does not remain perfectly centralized from the control motor. Moreover, the system supports not only objects but also human beings that may jump or otherwise create complex acceleration and velocity vectors that induce swinging motion of the lifting cable. While current literature discusses moving swinging pendulum systems, which in the current literature can be referred to cart-pendulum system, suitable solutions to the aforementioned problems of the first generation ARGOS system are not found in the prior art.
The following prior art references disclose various gravity and suspension systems but do not address the problems discussed hereinbefore:
U.S. Pat. No. 8,152,699 issued Apr. 10, 2012 to Ma, et al. discloses an apparatus and method for gravity-balanced apparatuses for training humans for space exploration and other applications. The present invention is statically-balanced and comprises a spring apparatus that is adjusted. An embodiment of the present invention provides an apparatus and method for simulating walking in a zero-gravity or reduced-gravity environment.
U.S. Pat. No. 7,199,790 issued Apr. 3, 2007 to Rosenberg, et al. discloses a method and apparatus for providing force feedback to a user operating a human/computer interface device in conjunction with a graphical user interface (GUI) displayed by a host computer system. A physical object, such as a joystick or a mouse, controls a graphical object, such as a cursor, within the GUI. The GUI allows the user to interface with operating system functions implemented by the computer system. A signal is output from the host computer to the interface device to apply a force sensation to the physical object using one or more actuators. This desired force sensation is associated with at least one of the graphical objects and operating system functions of the graphical user interface and is determined by a location of the cursor in the GUI with respect to targets that are associated with the graphical objects. The graphical objects include icons, windows, pull-down menus and menu items, scroll bars (“sliders”), and buttons. The force sensation assists the user to select a desired operating system function or physically informs the user of the graphical objects encountered by the cursor within the GUI. A microprocessor local to the interface apparatus and separate from the host computer can be used to control forces on the physical object.
U.S. Pat. No. 6,743,019, issued Jun. 1, 2004 to Ransom, et al., discloses a method and apparatus for aircraft-based simulation of variable accelerations and reduced gravity conditions. A test chamber is pivotally suspended in an aircraft, so that the center of gravity of the test chamber always self-actingly orients itself in the direction of the effective residual acceleration. To simulate a selected acceleration greater than 0 g and less than 1 g, the aircraft is flown along a parabolic flight path with a downward vertical acceleration such that the difference between Earth's gravitational acceleration and the aircraft's acceleration corresponds to the selected acceleration to be simulated. To simulate gravitational conditions on Mars, the aircraft is flown with a downward vertical acceleration of about ⅔ g, so that the residual acceleration acting on the test chamber is about ⅓ g. The atmospheric conditions, such as the gas composition, pressure and temperature, of Mars can also be established in the test chamber.
U.S. Pat. No. 6,566,834, issued May 20, 2003 to Albus, et al. discloses a modular suspended manipulator to manipulate tools and loads using position, velocity and force control modes. The manipulator includes a plurality of cables (2 or more) that are independently controlled by modular, winch drive-mechanisms and coordinated to achieve intuitive manipulator movement in all six degrees-of-freedom. The manipulator consisting of modular sub-assemblies and components (i.e. winch, amplifier, servo interface, sensory feedback), can be reconfigured to adjust to new applications. Various combinations of manual and automatic control can also be implemented. The winches can be controlled manually by a multi-axis joystick, or can be automatically controlled by computer.
U.S. Pat. No. 5,379,657, issued Jan. 10, 1995 to Hasselman, et al., discloses a method and system for supporting a test article or structure in a gravity environment for the purpose of testing the article in a simulated weightless condition and includes at least one support assembly attached to the article for suspending the article from an overhead support. The support assembly includes three cables each having an end attached to the article. The cables are capable of being actuated to cooperatively maintain a constant resultant vertical force on the test article which is equal to the weight of the article. The system includes a controller which is capable of adjusting the force in each cable to continuously maintain the constant resultant force on the article as it moves from position to position. The controller can calculate the new position of the test article as it moves from position to position. The controller is able to calculate each new position, calculate the forces necessary to maintain the constant resultant force on the test article, and actuate the cables to develop the required cable forces to offset the weight of the test article as the test article moves from position to position. The system can also use a plurality of such support assemblies to handle large size test structures.
U.S. Pat. No. 4,860,600, issued Aug. 29, 1989 to Schumacher, discloses a machine system that enables close duplication of three of the six weightless degrees of freedom of a space environment in the gravity field on earth's surface. The three degrees of freedom are two translational degrees of freedom orthogonal to the gravity vector and one rotational degree of freedom parallel to the gravity vector. The mechanism concept that duplicates the weightless environment eliminates all but air bearing forces acting on the object being tested in the plane orthogonal to the gravity vector without adding significant mass to the test object or confining the test object translational or rotational movements in the plane orthogonal to the gravity vector. The machine consists of at least three test object support platforms which permit small test object movements relative to the support platform without applying forces to the test object. The test object movements relative to each support platform are sensed and used to control two support platform translational degrees of freedom to maintain the support platform position relative to the test object.
United States Patent Application No. 2011/0088586, published Apr. 21, 2011 to Huang, et al., discloses a system, method, and apparatus for providing a reduced or moderated gravity environment in a terrestrial payload. The system includes the evaluation of terrain to support an appropriately shaped vehicle guide, the construction of a vehicle guide, the provision of a high-speed vehicle and a control system adapted to control a motion of the vehicle across the vehicle guide with a specific velocity profile so as to produce a moderated gravity environment.
United States Patent Application No. 2010/0279255, published Nov. 4, 2010 to Williams II, discloses a vehicle simulation system may include: a platform positioned within a three-dimensional workspace, at least six upper support members positioned outside the three-dimensional workspace, at least six upper adjustable cables routed from corresponding upper support members and secured to the platform to apply at least a portion of upward tension to the platform, and a vehicle secured to the platform. The vehicle may provide one or more occupants with a simulated experience within a three-dimensional virtual environment as the upper adjustable cables are adjustably extended and retracted in a coordinated fashion to maneuver the platform.
Japanese Patent No. JP3213500, issued Sep. 9, 1991 to Kawasaki Heavy Ind. Ltd., discloses a gravity-free simulating device in which an active drive mechanism is located on a ground, and a test piece is mounted on the active drive mechanism through a sensor to detect a force and torque. The sensor is arranged so as to allow detection of the forces of the X-Z axes and torque around the X-Z axes. The active drive mechanism is formed so that an object can be actively driven in orientation to roll, pitch, and yaw around each of X-Z axes. Feedback control is made on the active drive mechanism so that a force and torque detected by the sensor are balanced with gravity of the test piece, and feed forward control is effected according to the speed detecting value of the test piece.
The above cited prior art does not solve the aforementioned problems. Accordingly, there exists a need for an improved active response gravity offload system. Consequently, those skilled in the art will appreciate the present invention.